12 If I have told you earthly things and you do not believe, how will you believe if I tell you heavenly things?
This verse is a pointed rebuke of Nicodemus and of all Israel’s proclivity toward legalistic self-righteousness.
12 If [and it is true] I have told you earthly things and you do not believe,
Jesus now turned to explain confusion over His statements about being born again. He set forth the doctrine of being born again in earthly terms but it was not understood. Human beings by human means cannot come to God.
Jesus now argued from the lesser to the greater. If Nicodemus and Israel could not understand Jesus’ simple illustrations about being born again, how could they grasp the greater and more abstract issue about spiritual regeneration? “Earthly things” refers to illustrations such as the “wind” that Jesus gave about spiritual birth (Jn 3:8).
Nicodemus’ surface belief in Jesus as a mere teacher was completely inadequate. He refused to “believe” in what Jesus said and who He was. The word “believe” occurs twice in this verse. Belief is a central issue in the gospel of John and foundational to everything about Jesus.
how will you believe if I tell you heavenly things?
Since Nicodemus did not grasp the illustrations that Jesus had just given about what it meant to be born again, how could he come to grips with greater realities about God’s plan of salvation?
“Heavenly things” refers to the economy of salvation. If Nicodemus could not understand the concrete illustrations that Jesus gave, how was it possible for him to grasp the abstract idea of new birth?
Failure to believe is more reprehensible than failure to understand.
Jesus introduced Nicodemus to the idea of regeneration, but this teacher of Israel refused to believe it. Refusal to believe that Jesus is God and that we are in need of His salvation is at the heart of why people will spend eternity in hell.
Jesus never allows for justification for unbelief or excuses like that of Nicodemus. Positive volition is always the issue for our Lord; we either accept or reject truth. Jesus expects decisiveness in our decision to believe on Him.